JP5188480B2 - Light source for sterilization - Google Patents

Description

  The present invention relates to a sterilization light source that is used for sterilization by emitting ultraviolet light having a specific wavelength using electrons emitted from an electron beam source.

Ultraviolet light is generally referred to as ultraviolet light and is widely used for lighting, pest control, resin curing, and the like. In recent years, there has been an increasing interest in deep ultraviolet light having a wavelength of 200 to 350 nm and vacuum ultraviolet light having a wavelength of 200 nm or less. Among deep ultraviolet light, ultraviolet light of 250 to 270 nm is considered to have a high bactericidal effect against viruses, bacteria, and molds. The sterilization mechanism has also been studied, and it is said that ultraviolet light of this wavelength acts on DNA in the living body to lose its proliferation function. Using this bactericidal action, sterilizers have been developed for a wide variety of raw meat, processed fishery products, cooked rice, drinking water and hot water, factory wastewater and domestic wastewater, food and medical containers, It's being used.
However, these ultraviolet light sources include gases such as excimer lasers and various SHG lasers (second harmonic generation lasers) and ultraviolet lasers using solids as media; excimer lamps, xenon flash lamps, low-pressure mercury lamps, and other gases. Only lamps have been put to practical use. Since these are large-sized, have a short life span, and are expensive, they are difficult to apply to ordinary homes and medical care. Therefore, development of a compact, inexpensive, high-efficiency, long-life ultraviolet light source has been desired.
Currently, deep ultraviolet light emitting diodes using aluminum gallium nitride semiconductor materials are being developed. This material has a light emission region in the 200 to 360 nm band, is capable of high-efficiency light emission, and has characteristics such as a long lifetime of the element. However, until now, since a high-quality crystal of aluminum nitride serving as a base substrate of a light-emitting element could not be manufactured, a light-emitting efficiency is still low and a high-brightness deep ultraviolet light-emitting diode cannot be realized. In addition, this semiconductor light emitting diode requires complicated semiconductor conductivity control and a complicated device structure (PN structure or PIN structure).
By the way, a method is known in which high-purity hexagonal boron nitride is irradiated with an electron beam to emit deep ultraviolet light of 215 nm (Patent Document 1). On the other hand, there is a report on the light emission behavior of electron irradiation of lithium calcium aluminum aluminum fluoride (Ce: LiCaAlF ₆ ) containing cerium element, and it is described that ultraviolet light of 290 nm and 310 nm emits light (non-patent document). 1). Since light emission by these electron beam irradiations is performed by irradiating an electron beam to a massive crystal body, it is difficult to sterilize a large area. In addition, since the light emitting material is limited, there is a problem that light cannot be emitted near 260 nm, which is useful for sterilization.

JP 2005-228886 A

Y. Suzuki et al. , “Hybrid time-resolved spectroscopic system for evaluating laser material using a table-top-sized, low-jitter, 3-MeV picoseconds electron-beam source with a photocathode” Applied Physics Letters 2002,80, p3280-3282

  The present invention adopts a new light emitting means that has improved the disadvantages of the currently used light source for ultraviolet sterilization, that is, large size, large power consumption, short life, and unstable intensity. An object of the present invention is to provide a light source for sterilization having a simple structure.

  In view of the above circumstances, the present inventors examined the light emission characteristics of ultraviolet light for various crystal materials, and as a result, the metal fluoride crystals were used to make the film thin and combined with an electron beam source to satisfy the above characteristics. It has been found that it can be used as a light source for sterilization, and the present invention has been completed.

That is, according to the present invention,
A light emitting substrate composed of a transparent substrate and a metal fluoride thin film layer formed on the transparent substrate and an electron beam source are provided, and the metal fluoride layer of the light emitting substrate is irradiated with an electron beam, thereby being effective for sterilization. There is provided a sterilizing light source that generates light including deep ultraviolet light having a wavelength of 320 nm.
In the invention of the light source for sterilization,
The metal fluoride thin film layer is preferably a thin film layer made of a metal fluoride containing calcium fluoride, barium fluoride, or praseodymium (Pr).

  According to the present invention, it is possible to provide a light source for sterilization that can be sterilized with a small size, low power consumption, long life, and a simple structure, and can be suitably used in general households and medical fields. In addition, it can be expected that the field of application will dramatically expand as a compact, high-power portable sterilization light source.

It is a structural diagram of the light source for sterilization of this invention. It is a schematic structure figure of other examples of the light source for sterilization of the present invention. It is the schematic of a pulse laser deposition apparatus. It is the schematic of the sterilization apparatus incorporating the light source for sterilization of this invention. 2 is an emission spectrum diagram of a deep ultraviolet light emitter manufactured in Example 1. FIG. 6 is an emission spectrum diagram of the light-emitting device manufactured in Example 2. FIG. 7 is an emission spectrum diagram of the light-emitting device manufactured in Example 3. FIG.

  The light source for sterilization of the present invention is characterized in that it has an ultraviolet light emitting part with a very simple structure. The light source for sterilization includes a light emitting substrate composed of a transparent substrate and a metal fluoride thin film layer formed on the transparent substrate, and an electron beam source for generating an electron beam, and emits electrons from the electron beam source to the light emitting substrate. To generate light including deep ultraviolet light having a wavelength of 200 to 320 nm which is effective for sterilization.

  FIG. 1 schematically shows the basic structure of this sterilizing light source. The light emitting substrate includes a transparent substrate 5 and a metal fluoride thin film 4 formed on the transparent substrate, and is arranged in the order of the electron beam source 1, the anode 3 described later, the metal fluoride thin film 4, and the transparent substrate 5. A light source for sterilization is formed. In FIG. 1, the transparent substrate 1 also serves as the window member of the vacuum vessel 6 that is the housing of the sterilization light source of the present invention, but as shown in FIG. 2, a separate window member 7 is provided instead of the transparent substrate 1, A light-emitting substrate composed of the transparent substrate 5 and the metal fluoride thin film layer 4 formed on the transparent substrate 5 may be installed inside the vacuum container 6 of the sterilization light source of the present invention.

  The transparent substrate 5 constituting the light emitting substrate needs to transmit 200 to 320 nm deep ultraviolet light generated from the metal fluoride thin film layer 4 by irradiating electrons. The transparent substrate also serves as a base substrate for forming and holding the metal fluoride thin film. The structure shown in FIG. 1 also serves as a window member. Examples of materials having such properties include quartz, quartz glass, sapphire, fluoride glass, lithium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Glass, calcium fluoride, and the like are preferable in that a large-area substrate can be easily manufactured.

  The thickness of the transparent substrate 5 is not particularly limited, but is preferably in the range of 0.1 to 20 mm from the viewpoint of strength and transparency. In particular, when it also serves as a window member, it is preferably in the range of 1 to 10 mm from the viewpoint of strength, and when a separate window member is provided, the strength is not necessary so that it is preferably 0.1 to 1 mm. The area of the transparent substrate 5 is not particularly limited, and depends on the area on which the metal fluoride thin film 4 to be described later is to be provided. The larger the thin film layer 4 and the transparent substrate 5, the larger the area of the light source for sterilization.

  A metal fluoride thin film layer 4 is formed on the transparent substrate 5. The electrons emitted from the electron beam source 1 are applied to the thin film layer 4 to emit deep ultraviolet light from the thin film layer 4, and then the deep ultraviolet light passes through the transparent substrate 5 (when a separate window member is provided). Is further transmitted through the window member) and irradiated outside the light source for sterilization of the present invention.

As the metal fluoride constituting the metal fluoride thin film 4, it is necessary to use a metal fluoride that emits deep ultraviolet light of 200 to 320 nm when irradiated with an electron beam. Examples of such a metal fluoride include CaF ₂ , SrF ₂ , and BaF ₂ that emit deep ultraviolet light of 200 to 320 nm by self-trapped exciton (STE). In addition, PrF ₃ and Pr-doped CaF ₂ , SrF ₂ , BaF ₂ , LaF ₃ , CeF ₃ , BaY ₂ F ₃ , KYF ₄ , KY that emit the deep ultraviolet light due to the 5d-4f transition of praseodymium (Pr). Examples thereof include metal fluorides such as ₃ F ₁₀ , YLiF ₄ , LuLiF ₄ , LiCaAlF ₆ , and LiSrAlF ₆ .

  The crystallinity of the metal fluoride thin film layer 4 is not particularly limited and may be amorphous, polycrystalline, or single crystal. However, when Pr is contained (doped), the higher crystallinity is the doping element. Since some Pr is likely to work as a luminescent center, it is preferably polycrystalline or single crystal. From the viewpoint of increasing the area of the metal fluoride thin film layer, it is preferably amorphous or polycrystalline.

  The lower limit of the film thickness of the metal fluoride thin film layer 4 is not particularly limited. However, the average thickness of the metal fluoride thin film layer 4 to be formed is preferably 100 nm or more in order to prevent the thickness of the metal fluoride thin film layer 4 from becoming non-uniform and causing a remarkably thin portion. Further, in terms of luminous efficiency, the thickness is preferably 1 μm or more. The upper limit of the film thickness is arbitrary, but it is preferably less than 10 μm on average from the viewpoints of maintaining crystallinity, reducing the size and weight, and reabsorbing light emission. The area of the metal fluoride thin film layer 4 to be formed is not particularly limited as long as it is too small to handle and form an anode. Rather, by increasing the size, light can be emitted in a large area, which can be a light source for sterilization that requires a large area.

  Such a metal fluoride thin film layer 4 can be operated as a light emitting substrate only by forming a single layer on the transparent substrate 5, but it is not always necessary to be a single layer film, and a multilayer film can also be used. For example, the crystallinity of the metal fluoride thin film layer 4 can be improved by forming some buffer layer that eliminates the lattice mismatch between the transparent substrate 5 and the metal fluoride thin film layer 4. Further, an antioxidant film may be formed on the outermost surface (the deep ultraviolet light emission surface side) of the light emitting substrate.

  The method for producing the metal fluoride thin film layer 4 is not particularly limited, and a known crystal growth method or thinning method can be used. Specifically, a pulse laser deposition method (laser ablation method), a molecular beam growth method in which crystals are grown from a molecular material evaporated in a vacuum, or a crystal material is dissolved in a metal that has become liquid at high temperature to become a seed. It is possible to use a method such as an LPE method or a sputtering method in which a crystal is grown on the substrate by putting the substrate and cooling. Moreover, it is good also as a thin film layer which consists of metal fluoride powder. Among these, the pulse laser deposition method which is a kind of vapor phase growth method is preferable. The pulse laser deposition method is a physical vapor deposition method in which a raw material is given a large energy by laser pulse irradiation to be sublimated and deposited on a substrate. This method is easy to produce a thin film with uniform optical properties, and therefore has uniform light emission performance, compared to chemical vapor deposition, which tends to make the optical properties of the formed thin film non-uniform. Are better.

  Hereinafter, a specific description of forming the metal fluoride thin film layer 4 on the transparent substrate 5 will be given with reference to FIG. 3 by taking a pulse laser deposition method as a typical vapor phase growth method as an example. The pulse laser deposition method is one of physical vapor depositions using laser light as an energy source for material evaporation, and is also called a laser ablation method. A high-power pulsed laser beam is incident from the laser light source 8, focused and irradiated on the surface of the target 9, and the instantaneous peeling (ablation) of the surface layer portion that occurs at that time is used to make atoms, molecules, In this film forming process, ions and clusters are deposited on the transparent substrate 10. The target 9 may be a single crystal, polycrystal, pellet or the like of the metal fluoride described above. The laser light source 8 may be a third harmonic of an Nd: YAG laser.

  On the metal fluoride thin film layer 4, the anode 3 is usually installed for the purpose of extracting and accelerating electrons from the electron beam source. As the anode 3, a thin metal plate, a metal film, or a conductive metal oxide film can be used. The film thickness is not particularly limited, but it is preferably 1 nm or more because of minimum durability, and is preferably 1000 μm or less from the viewpoint of reduction in size and weight. Alternatively, a multilayer film may be formed using a plurality of metals or metal oxides. As the material of the anode 3, conventionally known metals and conductive oxides can be arbitrarily used. Specifically, it consists of at least one of aluminum, titanium, nickel, cobalt, gold, silver, copper, chromium, ITO (indium tin oxide), and the like.

  As a method of forming a metal film or a metal oxide film on the metal fluoride thin film layer 4, a conventionally known metal film forming technique can be arbitrarily used. Specifically, a vacuum deposition method can be used. The vacuum vapor deposition method is a method of forming a uniform film sample by depositing particles generated by sublimation or evaporation of a vapor deposition material by heating in vacuum in a substrate. By using a shield called a mask, a portion that is not desired to be deposited can be shielded to form an anode having an arbitrary shape. Moreover, it can also be set as the anode 3 as a desired shape by machining a metal thin plate.

  There is no particular limitation on the shape of the anode. However, since it is necessary for the electron beam to pass through the anode 3 and reach the metal fluoride thin film layer 4, a mesh-shaped or slit-shaped anode is preferable. When the anode is formed on the entire surface of the metal fluoride thin film 4, all the electron beams irradiated from the electron source are captured by the anode 3 and do not emit light. The anode 3 may be formed on the surface of the transparent substrate 5 opposite to the surface on which the metal fluoride thin film layer 4 is formed. In that case, the anode 3 is formed on the metal fluoride thin film layer 4. It is necessary to apply a large voltage.

An electron beam for emitting deep ultraviolet light is irradiated from the electron beam source 1. As the electron beam source 1, a conventionally known tungsten electron filament, lanthanum boride (LaB ₆ ) filament or the like is used. A thermoelectron gun using electrons emitted when a metal is heated to a high temperature; carbon nanotube or diamond A field emission electron gun (field emitter) that utilizes electrons emitted by applying an electric field to a solid surface such as silicon or silicon is employed. A field emitter is preferable because no heat is generated, the voltage is low, power is saved, and the light source for sterilization can be miniaturized because the thickness can be reduced. When the electron beam source 1 is a field emitter, the field emitter itself becomes a cathode.

The aforementioned field emitter needs to be held in a vacuum. If the degree of vacuum is low, the field emitter is sputtered and tends to deteriorate. Therefore, it is preferable to set the degree of vacuum so that sputtering does not occur. Specifically, the light emitting substrate and the electron beam source 1 are installed in the vacuum vessel 6, and the inside of the vacuum vessel 6 is preferably in a vacuum state of preferably 1 Pa or less, more preferably 1 × 10 ⁻³ Pa or less. Is adopted.

When a field emitter is used as the electron beam source 1, for example, a voltage of 100 V to 10 kV can be applied between the field emitter and the anode 3 at an electron density of 1 to 100 mA, depending on the material and shape of the field emitter and the distance from the anode. That's fine.
The light source for sterilization of the present invention emits deep ultraviolet light having a wavelength of 200 to 320 nm. For example, when CaF ₂ is used as the metal fluoride, ultraviolet light including deep ultraviolet light in the wavelength range of 230 to 320 nm having a peak in the vicinity of the wavelength 280 is emitted.

  The light emitting substrate and the electron beam source 1 are integrated with other necessary members such as the anode 3 to constitute a light source for sterilization. The light source for sterilization is incorporated as a deep ultraviolet light source to form a sterilizer. However, a known device structure can be adopted, and the sterilizer of the present invention can be used instead of the low-pressure mercury lamp disposed in the existing sterilizer. A light source may be installed.

Specifically, in the case of water sterilization treatment, the light source for sterilization of the present invention is installed in a tank, and a pump, a filter, a heater and a cooler for transporting water are provided as necessary. The light source for sterilization can be arbitrarily designed in accordance with the type of object to be treated, transparency, etc., such as a completely immersed structure, a semi-immersed structure, or a structure irradiated from the upper surface of water.
Of course, it can be applied not only to the sterilization treatment of water but also to the treatment of other objects. For example, when the object is water or hot water of a vending machine, the sterilization apparatus described in JP-A-2004-50003 is used. In the case of raw meat or processed fishery products, the sterilization apparatus described in Japanese Patent Laid-Open No. 8-242929 is used, and in the case of sterilizing the inner and outer surfaces of food containers and medical containers, the sterilization apparatus described in Japanese Patent Laid-Open No. 9-201401 is used without any limitation. In place of the ultraviolet lamps of these existing apparatuses, the sterilization light source of the present invention can be arranged.

  The light source for sterilization according to the present invention can be arranged three-dimensionally in accordance with the shape of the object to be sterilized, or can be arranged in parallel in the horizontal or vertical direction. In this respect, since the light source for sterilization of the present invention is a device that is extremely small and can have a large area, the degree of freedom of the combination is very high as compared with an existing ultraviolet lamp having a long diameter.

  For example, as shown in FIG. 3, by providing a zigzag water channel having a plurality of bent portions on the surface of the light source for sterilization of the present invention, a wide sterilization region can be provided on the light emitting surface of a large area, and the sterilization time Can be lengthened. At this time, another light source for sterilization may be installed so as to sandwich the water channel.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In addition, not all combinations of features described in the embodiments are essential to the solution means of the present invention.

Example 1
[Formation of metal fluoride thin film on transparent substrate]
A calcium fluoride (CaF ₂ ) thin film was produced on a quartz glass substrate using a pulse laser deposition apparatus. Quartz glass of 20 × 20 × 0.5 (width × length × thickness, unit mm) was used for the substrate. A CaF ₂ sintered body was used as the target. First, the inside of the chamber was evacuated to about 2.0 × 10 ⁻⁴ Pa using a rotary pump and an oil diffusion pump. Next, in a state where the substrate and the target are shielded by a metal plate so that film formation is not performed, the target is irradiated with a pulse laser having a wavelength of 355 nm and a repetition frequency of 10 Hz, and the target surface layer on which impurities may be attached After peeling and removing for 10 minutes, the metal plate between the substrate and the target was removed to form a film. The distance between the target and the substrate is 4.2 cm, the deposition time is 240 minutes, the film formation is performed at a substrate temperature of 400 ° C., and the energy amount of laser irradiation per unit area is 15.5 (J / cm ² ). went. Incidentally, the energy of laser irradiation per unit area of the pulse energy E of the experiment and the width D of the laser irradiation signatures of the target after laser irradiation, was calculated as E ^/ πD ^2/4. The pulse energy E is based on the average laser power P during the experiment.
E (J) = P (W) / 10 (Hz),
It was calculated from the following formula. When the film thickness of the metal fluoride thin film produced under these film forming conditions was evaluated by observing a cross-sectional SEM image, it was 300 nm.

[Production of light source for sterilization]
Next, from above, a quartz glass substrate, a CaF ₂ thin film, a 0.05 mm thick mesh copper plate anode (0.1 mm wide electrodes arranged in a 0.1 mm gap), a 0.1 mm thick Teflon spacer, The carbon nanofiber field emitters were arranged in this order, and these were sandwiched between Teflon plates and fixed. This was enclosed in a vacuum container using quartz glass as a window member (thickness 3 mm) to obtain a light source for sterilization with a vacuum degree of 4 × 10 ⁻⁴ Pa or less.

[Deep ultraviolet emission characteristics of sterilization light source]
The sterilization light source thus produced was connected to an electrometer. Keithley Electrometer Model 6517 was used as the electrometer. A deep ultraviolet emission spectrum was measured by applying 770 V to the sterilizing light source from a power source with a built-in electrometer. The spectrum measurement was performed using an EPP2000-UVN-SR compact spectroscope manufactured by Stellarnet, through an F1000-UV-VIS-SR optical fiber. The obtained emission spectrum is shown in FIG.

Example 2
[Formation of metal fluoride thin film on transparent substrate]
PrF ₃ powder and CaF ₂ powder were mixed with those pellets as a target: except for using _(PrF 3 1 mol%) in the same manner as in Example 1, Pr on a quartz glass substrate: 0.1 ml of the CaF2 film . The film thickness was 100 nm.

[Production of devices]
A light source for sterilization was produced in the same manner as in Example 1.

[Device emission characteristics]
The emission spectrum of the produced sterilizing light source was measured in the same manner as in Example 1 except that the applied voltage was set to 1000V. The obtained emission spectrum is shown in FIG.

Example 3
[Formation of metal fluoride thin film on transparent substrate]
A BaF ₂ thin film was produced on a quartz glass substrate in the same manner as in Example 1 except that a target obtained by melting and solidifying BaF ₂ powder was used. The film thickness was 100 nm.

[Production of devices]
A light source for sterilization was produced in the same manner as in Example 1.

[Device emission characteristics]
The emission spectrum of the produced sterilizing light source was measured in the same manner as in Example 1 except that the applied voltage was set to 1000V. The obtained emission spectrum is shown in FIG.

DESCRIPTION OF SYMBOLS 1 Electron beam source 2 Spacer 3 Anode 4 Metal fluoride thin film layer 5 Transparent substrate 6 Vacuum container 7 Window member 8 Laser light source 9 Target 10 Transparent substrate 11 Light source for sterilization 12 Water channel

Claims (2)

  A light emitting substrate composed of a transparent substrate and a metal fluoride thin film layer formed on the transparent substrate and an electron beam source are provided, and the metal fluoride layer of the light emitting substrate is irradiated with an electron beam, thereby being effective for sterilization. A light source for sterilization characterized by generating light including deep ultraviolet light having a wavelength of 320 nm.   The light source for sterilization according to claim 1, wherein the metal fluoride thin film layer is a thin film layer made of a metal fluoride containing calcium fluoride, barium fluoride, or praseodymium (Pr).

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